Imipenem-Cilastatin Sodium
Imipenem monohydrate / Cilastatin sodium
Also known as: Primaxin · Klonam · Tenacid · Tienam · Tracix · Zienam · N-formimidoyl thienamycin · imipemide · MK-787 · MK-0787
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible infections | 5-10 mg/kg | IV, SC or IM | q8h | — | 🌎 NA |
| Susceptible infections | 5-10 mg/kg | IV or IM | q6h | — | 🌎 NA |
| Tissue infections | 3-7.5 mg/kg | IV, SC or IM | q4-6h | 3-5 days | 🌎 NA |
| Sepsis, more resistant organisms | 5 mg/kg | IV | q4h | 3-5 days | 🌎 NA |
| Treatment of Nocardiosis | 2-5 mg/kg | IV | q8h | — | 🌎 NA |
- Susceptible infections: IM form is different
- Susceptible infections: IV given over 30 minutes. IM mixed with 1% lidocaine to reduce pain. Cannot interchange IV and IM dosage forms.
- Sepsis, more resistant organisms: Multi-drug resistant bacteria may require q2h dosing
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible infections | 5-10 mg/kg | IV, SC or IM | q8h | — | 🌎 NA |
| Susceptible infections | 5-10 mg/kg | IV or IM | q6h | — | 🌎 NA |
| Tissue infections | 3-7.5 mg/kg | IV, SC or IM | q4-6h | 3-5 days | 🌎 NA |
| Sepsis, more resistant organisms | 5 mg/kg | IV | q4h | 3-5 days | 🌎 NA |
| Treatment of Nocardiosis | 2-5 mg/kg | IV | q8h | — | 🌎 NA |
- Susceptible infections: IM form is different
- Susceptible infections: IV given over 30 minutes. IM mixed with 1% lidocaine to reduce pain. Cannot interchange IV and IM dosage forms.
- Sepsis, more resistant organisms: Multi-drug resistant bacteria may require q2h dosing
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible infections (Adult horses) | 10-20 mg/kg | IV | q6h | — | 🌎 NA |
| Susceptible infections (Foals) | 10-20 mg/kg | IV | q6h | — | 🌎 NA |
| Susceptible infections (Foals) | 10-15 mg/kg | IV or IM | q6-12h | — | 🌎 NA |
- Susceptible infections (Adult horses): Give via slow IV over a 10 minute period. Alternatively, a CRI of 16 micrograms/kg/minute should maintain synovial concentrations > 1 microgram/mL.
- Susceptible infections (Foals): IM if diluted into 1% lidocaine. May give as a CRI at 0.4-0.8 mg/kg/hr.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Imipenem-cilastatin is a potent, broad-spectrum intravenous/intramuscular antimicrobial combination reserved for serious, life-threatening, or multi-drug resistant infections in veterinary medicine.
- Imipenem is a carbapenem antibiotic with an exceptionally broad spectrum of activity, including gram-positive, gram-negative, and anaerobic bacteria. It is particularly valuable against resistant gram-negative organisms like Pseudomonas aeruginosa and Enterobacteriaceae (e.g., ESBL-producing strains).
- Cilastatin is a dehydropeptidase I (DHP I) inhibitor. It has no antibacterial activity itself but is crucial because it prevents the rapid degradation of imipenem by enzymes in the kidneys.
Clinical Pearl: Because of its broad spectrum and importance in treating highly resistant infections, imipenem is considered a "big gun" or reserve antibiotic. Its use should ideally be guided by culture and susceptibility testing to prevent the emergence of carbapenem-resistant bacteria.
Mechanism of action
The drug functions through a synergistic two-part mechanism:
- Imipenem (Bactericidal Action): Imipenem penetrates bacterial cell envelopes and binds with high affinity to penicillin-binding proteins (PBPs) (specifically PBP-2 and PBP-1B in gram-negative bacteria) → inhibits peptidoglycan cross-linking → disrupts bacterial cell wall synthesis → leads to cell lysis and death.
- Cilastatin (Pharmacokinetic Enhancer): Imipenem is normally rapidly metabolized by dehydropeptidase I (DHP I), an enzyme located on the brush borders of the proximal renal tubules. Cilastatin competitively inhibits DHP I → prevents imipenem degradation → ensures high, therapeutic antibacterial concentrations in the urine and protects the patient from proximal renal tubular necrosis that can occur if imipenem is administered alone.
Safety & warnings
Contraindications
- Patients with known hypersensitivity to imipenem, cilastatin, or other beta-lactam antibiotics (due to partial cross-reactivity)
- Caution in patients with renal impairment (dosage adjustment required)
- Caution in patients with underlying CNS disorders (e.g., seizures, head trauma) due to increased risk of neurotoxicity
Adverse effects
- Gastrointestinal upset (vomiting, anorexia, diarrhea)
- CNS toxicity (seizures, tremors)
- Hypersensitivity reactions (pruritus, fever, anaphylaxis)
- Infusion reactions (thrombophlebitis)
- Severe pain and potential neurovascular damage at IM injection sites
- Transient increases in BUN, serum creatinine, AST, ALT, and Alkaline Phosphatase
- Hypotension or tachycardia (rare)
Precautions
CRITICAL WARNINGS:
- Do NOT administer via rapid IV infusion. Rapid infusion significantly increases the risk of CNS toxicity and seizures. Doses ≤ 500 mg should be given over 20-30 minutes; doses > 500 mg should be given over 40-60 minutes.
- Formulation Specificity: The IV and IM dosage forms are NOT interchangeable. If giving IM or SC, the specific IM product must be used.
- Renal Impairment: Animals with reduced renal function (including neonates and geriatrics) are at a higher risk for seizures. Dosages may need to be reduced or dosing intervals extended.
- IM Administration: Can cause severe pain. It is recommended to dilute the IM form in 1% lidocaine (without epinephrine) to relieve associated pain.
Drug interactions
Additive effects or synergy may result, particularly against Enterococcus, Staph. aureus, and Listeria monocytogenes. No synergy or antagonism noted against Enterobacteriaceae or Pseudomonas aeruginosa.
Antagonism may occur against several Enterobacteriaceae (including Pseudomonas aeruginosa, Klebsiella, Enterobacter, Serratia). Concurrent use is not recommended.
May antagonize the antibacterial effects of imipenem (based on in vitro evidence).
May increase concentrations and elimination half-life of cilastatin, but not imipenem; concurrent use is not recommended.
Synergy may occur against Nocardia asteroides when used in combination.
Monitoring
- Clinical efficacy (resolution of infection signs)
- Adverse effects (especially CNS signs like tremors or seizures)
- Renal and hepatic function tests (BUN, creatinine, AST, ALT, Alk Phos) if treatment is prolonged or if the patient has pre-existing organ dysfunction
Pharmacokinetics
Half-life
Absorption
Not absorbed appreciably from the GI tract. Bioavailability after IM injection is ~95% for imipenem and 75% for cilastatin. In dogs, SC bioavailability of imipenem is complete.
Distribution
Distributed widely throughout the body, with the exception of the CSF. Crosses the placenta and is distributed into milk.
Metabolism
Imipenem is metabolized by dehydropeptidase I (DHP 1) in the kidneys; this metabolism is inhibited by the concurrent administration of cilastatin.
Elimination
Eliminated by both renal and non-renal mechanisms. Approximately 75% of a dose is excreted in the urine and about 25% by unknown non-renal mechanisms.
Overdose
Information on acute toxicity is limited. The LD50 of imipenem:cilastatin (1:1 ratio) in mice and rats is approximately 1 gram/kg/day.
Management:
- Halt therapy immediately.
- Provide supportive and symptomatic care (e.g., anticonvulsants if seizures occur, fluid therapy to support renal clearance).
Available products
Formulations
- Powder for Injection (IV)
- Powder for Injection (IM)
Human-labeled
- Imipenem Cilastatin Powder for Injection: 250 mg imipenem / 250 mg cilastatin (Primaxin I.V.)
- Imipenem Cilastatin Powder for Injection: 500 mg imipenem / 500 mg cilastatin (Primaxin I.V.)
- Imipenem Cilastatin Powder for Injection: 500 mg imipenem / 500 mg cilastatin (Primaxin I.M.)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store commercially available sterile powders at room temperature (<25°C). After reconstitution, IV solutions are stable for 4 hours at room temperature or 10 hours when refrigerated. Do not freeze. The IM suspension (reconstituted with 1% lidocaine) must be used within one hour.
Client information
What you need to know about Imipenem-Cilastatin:
- Hospital Setting: This is a highly specialized, potent antibiotic typically reserved for severe or highly resistant infections. It is almost exclusively administered in a veterinary hospital setting where your pet can be closely monitored.
- Administration: It must be given by injection (usually through an IV catheter or into the muscle). If given into the muscle, it may cause some pain, so the veterinarian may mix it with a local anesthetic to make your pet more comfortable.
- Side Effects: While generally safe when monitored, it can cause stomach upset (vomiting, loss of appetite, diarrhea). Rarely, it can cause neurological signs like tremors or seizures. If you are visiting your pet and notice any twitching or unusual movements, notify the veterinary staff immediately.
- Cost: Because this is an advanced, human-grade hospital antibiotic, treatment can be quite expensive. Your veterinarian will discuss the estimated costs with you.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.